The present invention relates to a motor-driven power steering unit with an electric motor for producing an auxiliary steering force in a steering system that couples a steering handle to the wheels of a vehicle, whereby the power steering unit assists the rotation of the steering wheel by controlling an electric current fed to the electric motor based on steering information comprising a steering angle detection device.
A generic motor-driven power steering unit is known from DE 38 21 789. This power steering unit comprises a steering force protection device for detecting the steering force produced in the steering system as well as an overload protection device to reduce the electric current fed to the electric motor. On the basis of the steering force detected, which is measured, for example, on the torsion bar of the steering system, the support is reduced by means of the overload protection device if the steering force detected exceeds a pre-determined angle. In addition, DE 38 21 789 discloses a generic power steering unit, in which additionally the steering speed is measured and this variable is also considered in the computation or reduction of the support. With this embodiment, the support is only reduced if, on the one hand, the hand force level is exceeded and, on the other hand, the steering speed has not exceeded a certain value. The power steering units known from DE 38 21 789 have the disadvantage that the driving feel at the end stop is determined by the rotational rigidity of the torsion bar of the steering system and cannot be influenced or regulated by controlling the power steering unit.
Object of the present invention is to create a power steering unit, in which the driving feel within range of the left and right end stop can be influenced in a pre-determinable way i.e. by a corresponding reduction of the support.